Electrical protective device



I P. MAcGAHAN. ELECTRICAL PROTECTWE DEVICE.

APPLICATION FILED JULY 6.19"

Patented Aug. 12, 1919.

. INVENTOR b: RM/7am; FQ BY ATTORNEY.

WITH E5555 2 WM UNITED STATES PATENT OFFICE.

PAUL MAOGAHAN, OF PITTSBURGH, PENNSYL'IAIN'IA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

ELECTRICAL PROTECTIVE DEVICE.

Specification of Letters Patent.

Patented Aug. 12, 1919.

Application flied July 6, 1917. Serial No. 178,920.

To all whom it may concern:

Be it known that I, PAUL MACGAHAN, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Electrical Protective Devices, of which the following is a specification.

My invention relates to electrical protective devices and particularly in means for protecting parallel-connected transmission circuits.

One object of my invention is to provide means for protecting parallelconnected transmission circuits that are traversed by different values of current.

Another object of my invention is to rovide a single relay for the correspon in ends of a system of the above-indicate character that shall be adapted to selectively control the circuit interrupters of the parallel-connected circuits.

Heretofore, it has been the practice to protect parallel connected transmission circuits by operatively connecting the same together and providing relays across the equal potential points of the connecting means. Such devices will not function properly unless the loads on the various parallelconnected circuits are normally equal.

In view of the above, I provide means whereby a plurality of parallel-connected circuits that are traversed by diflerent values of current may be protected. In practising my invention, I connect a resistor or auto transformer across the connecting means between the corresponding conductors of the parallel-connected circuits and so ad'ust the same that equal-potential points will obtain irrespective of the normal variation in the energy traversing the various circuits. The current winding of a singlephase reverse energy relay is connected to the equal-potential points and adapted to selectively control the circuit interrupters in the several parallel-connected circuits.

In the accompanying drawings, Figure 1 is a dia arnmatic view of an electrical circuit em odymg my invention, and Fi 2 is a diagrammatic view of an electrics ,cir-

cuitembodying a modified form of my invention.

A generator 1 is connected to bus bars 2 and 3 which are connected through two parallel connected transmission or feeder circuits 4 and 5- to a load circuit 6.

The transmission circuit 4 comprises two conductors 7 and 8 that are provided with circuit interrupters 9 and 10 at the res ective ends thereof. Similarly, the circuit 5 comprises two conductors 11 and 12 that are provided with circuit interrupters 13 and 14 at the respective ends thereof. It may be assumed, for purposes of explanation, that the circuit 4 is of less impedance than the circuit 5 and, consequently, is traversed by relatively more current. The circuits 4 and 5 are provided with similar current transformers 15 and 16, and 17 and 18, respectively, at the respective ends thereof. One terminal of the transformer 15 is connected to one terminal 19 of a resistor 20 the other terminal 21 of which is connected to one terminal of the transformer 17. The other terminal of the transformer 17 is connected to the terminal 19 of the resistor 20. The other terminal of the transformer 15 is connected to an intermediate point 22 of the resistor 20. Similarly, one terminal of the transformer 16 is connected to one terminal 23 of a resistor 24 the other terminal 25 of which is connected to one terminal of the transformer 18. The other terminal of the transformer 18 is connected to the terminal 23 of the resistor 24, and an intermediate terminal 26 of the resistor 24 is connected to the other terminal of the transformer 16.

The intermediate terminal 26 of the resistor 24 is so located that the current through that portion of the resistor between the terminals 23 and 26 equals the difference between the currents in the circuits 4 and 5. That is, the drop in potential across this portion of the resistor must be equal to the drop in potential through the remaining portion thereof and of such sign that the total drop in potential between the terminals 23 and 25 is zero. Similary, the terminal 22 of the resistor 20 is so located that the drop in potential between the terminals 19 and 21. is zero. Thus, it will be readily seen that a number of equalpotcntial points will obtain across the cumulatively-connected circuits 27 and 28 between the respective transformers.

A reverse-energy relay 29 and an overload relay 30 are provided for controlling the circuits of the trip coils 31 and 32 ofthe circuit interrupters 10 and 14, respectively, and a reverse-energy relay 33 and an overload relay 34 are provided for controlling the circuits of the trip coils 35 and 36 of the circuit interrupter-s 9 and 10, respectively. The relays 29 and 33 severally comprise a current winding 37, a potential winding 38, that is connected across the conductors 7 and 8 or the bus bars, a meg'netizable core member 39, an armature 40,, a movable contact member 41, and stationary contact members 42 and 43. The relays 30 and 34 severally comprise a current winding 44, a magnetizable core member 45, an armature 46, a movable contact member 47 and a stationary contact member 48. The current windings 37 and 44 of the relays 29 and 30 are connected in series across the equal-potential points of the circuit 28 and the current windings 37 and 44 of the relays 33 and 34 are connected in series across the equalpotential points of the circuit 27.

Since the current windings of the relays are connected across normally equal-potential points and, since the resistors 20 and 24 maintain these points of equal potential, irrespective of the normally unequal division of the energy through the circuits 4 and 5 it will be seen that the contact members 0 the respective relays are normally held out of engagement. However, if a fault, such as a ground, occurs in the circuit 5, the current traversing the same will so change as to upset the normal circulation of current in the circuits 27 and 28 and, consequently, the condition of equal-potential points therein. This will cause the relay 29 to effect engagement between its contact members 41 and 43, and, if the current traversing the circuit 5 is of a predetermined value, the relay 30 will cause its contact member 47 to engage its stationary contact member 48, thus effecting the energization of the trip coil 32 from a source 49 of electromotive force to thereby trip the circuit interrupter 14. Similarly, the reversal of the current in the circuit 5 will effect the opening of the circuit interrupter 13.

Ifa ground obtains in the circuit 4, the relays 29 and 33 will cause their movable contact members 41 to engage their stationany contact members 42, and, if the overload is of a suflicient value, the relays 30 and 84 will cause their contact members 47 and 48 to be engaged and the trip coils 31 and 85 to be case iced to trip t a circuit inter-rupture 10 an 9. Thus, the relays 29 and 33 are adapted to selectively trip their respective circuit iuterruptcrs in accordance with the position of the fault on the circuits to be protected. 7

In Fig. 2 of the drawings, I have shown a modification of my invention wherein I have substituted an auto transformer 50 for the resistor 24 shown in Fig. 1 of the drawings. That is, the transformer 16 is conncctcd to points 51 and 52 thereon and the transformer 18 is connected to points 53 and 52 thereon. The current \viiuling 27 of the reverse-energy relay is connected to equalpotential points of a circuit 54, thus constituted, and is adapted to selectively control the tripping of the intcrruptcrs 10 and 1 1-, substantially as hereinbefore set forth. In this modification of my invention, I have shown the relay 29 alone controlling the trip coils, 31 and 32, because, in some instances, it is not essential that an overload relay be employed. It will, of course, be apparent that the auto transformer 50 is employed for the same purpose as the resistors 20 and 24, as shown in. Fig. 1 of the drawings. In other words, it is employed to n'iaintain equalpotential points in the circuit 54, irrespective of the normal difference in energy traversing the circuits 4 and 5.

My invention is not limited to the singlephase system illustrated, as it is applicable to any number of phases, and various modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim as my invention:

1. In an alternating-current system of distribution, the combination with parallel-connected feeder conductors carrying different values of current, and a current transformer for each conductor, of a resistor connected across one transformer and a portion thereof connected across another transformer, said resistor being so connected that equalpotential points are provided on the connectmg means.

2. In an alternating-current system of distribution, the combination with parallel-connected feeder conductors carrying; different values of current, and" a current transformer for each conductor, of a resistor so conneeted to the transformers that equal-potential points are provided on the connecting means.

3. In an alternating-current system of dis tribution, the combination with arallel-connected feeder conductors carrying different values of current, and a current transformer for each conductor, of an energyabsorbing means, means for connecting the said energy-absorbing means across one transformer and a portion thereof across another, whereby equalotential points are provided onthe connect 11g means.

' 4. The combination with parallel-com nected feeder, conductors carrying different values of current, circuit interrupters therefor, a transformer connected to each feeder conductor, and means for cumulatively connecting the transformers together, of means so connected across the said connecting means as to provide equal-potential points in the said connecting means.

5. The combination with arallel-connected feeder conductors carrying different values of current, circuit interrupters therefor, a transformer connected to each feeder conductor, and means for cumulatively connecting the transformers together, of a resistor so connected to the said connecting means as to provide equal-notential points on the said connecting means.

6. The combination with arallel-connected feeder conductors carrying different values of current, and a transformer connected to each conductor, of a resistor, means for connecting the resistor across the terminals of one transformer, and means for connecting a portion of the resistor across the terminal of another transformer whereby equal-potential points are produced in said first mentioned connectin means.

7. The combination wit two arallel-connected feeder conductors carrying difierent values of current, circuit interrupters therefor, a transformer connected to each feeder conductor, and means for operatively connecting the transformers at the corresponding ends of the conductors together, of means so connected to the connecting means as to provide equal-potential points therein, and a single relay connected across the equal-potential points for selectively controlling the interrupters.

8. The combination with two parallelconnected feeder conductors carrying different values of current, a circuit interrupter for each conductor, and a transformer connected to each conductor, of means for so connecting the transformers together that equal'potential points are provided on the connecting means, and a single relay having its current winding connected across the equal-potential points and its potential winding connected to the feeder conductors for selectively controlling; both interrupters.

9. The combination with two parallel-connected feeder conductors carrying different values of current, a circuit interrupter for each conductor, a series transformer for each conductor, and means for cumulatively connecting the same together, of means so connected to the said connecting means that equal-potential points are provided therein, and a single reverse-energ relay having its current winding connects across the equalpotential points and its potential winding connected to the feeder conductors for selectively controllin both interrupters.

In testimony w ereof, I have hereunto subscribed my name this 29th day of June PAUL MACGAHAN.

copies of thin potent may be obtained for five cents each, by addressing the Commissioner of Patents. Washington, .D. O. 

